Method and apparatus for making the human voice audible and comprehensible to severely deaf persons

ABSTRACT

A method and apparatus is provided for making the human voice audible and comprehensible to severely deaf persons which includes transforming an acoustic information signal corresponding to the human voice to corresponding electric signals, and summing these electric signals with a generated periodic signal or pseudo-carrier to provide a summation signal which is amplified and transformed to an acoustic signal. The method is based on the theory that the summation signal can pass through a diseased synapsis more easily than the separate information signal or the pseudo-carrier signal.

United States Patent [191 Biondi et al.

METHOD AND APPARATUS FOR MAKING THE HUMAN VOICE AUDIBLE AND COMPREHENSIBLE TO SEVERELY DEAF PERSONS Inventors: Emanuele Biondi, Via lppolito Nievo 28/1; Leonardo Biondi, Via Rontgen 19, both of Milan, Italy Filed: June 23, 1971 Appl. N0.: 156,109

Related U.S. Application Data Continuation-impart of Ser. No. 803,321, Feb. 28, 1969, abandoned.

U.S. Cl 179/107 R Int. Cl H04! 25/00 Field of Search 179/107 R, 107 BC,

179/107 S, 107 E, 107 H; 340/407 References Cited UNITED STATES PATENTS Mouzon 179/107 272/ "is/f) e I Dec. 25, 1973 3,385,937 5/1968 Lafon 179/107 R FOREIGN PATENTS OR APPLICATIONS 1,230,466 12/1966 Germany [79/107 R Primary Examiner-Kathleen l-l. Claffy Assistant Examiner-Thomas L. Kundert Attorney-Edwin E. Greigg [5 7] ABSTRACT 5 Claims, 6 Drawing Figures USCZ [L afar PMENIE BEBE 5 ma SHEET 2 BF 2 METHOD AND APPARATUS FOR MAKING THE HUMAN VOICE AUDIBLE AND COMPREHENSIBLE TO SEVERELY DEAF PERSONS This application is a continuation-in-part of our copending U.S. Pat. application Ser. No. 803,321, filed Feb. 28, 1969 and now abandoned.

BACKGROUND OF THE INVENTION The present invention relates to a method and apparatus for making the human voice audible and comprehensible to severely deaf persons.

Deafness is defined as the impairment, loss or lack of the sense of hearing. Deafness may occur in varying degrees and forms. For the purpose of this invention, when reference is made to severely or profoundly deaf persons, it is meant persons having a perceptive loss attributable to a defect, disease, or impairment of the central nervous part of the auditory system of such degree that natural speech, even if amplified through a conventional hearing aid, is meaningless noise to them.

SUMMARY OF THE INVENTION The method according to the present invention consists of summing a pseudo-carrier signal and an information signal so as to cause the summation signal to pass through a diseased synapses more easily than the individual pseudo-carrier or information signal. This method is based on applicants theory which may be referred to as the pseudo-carrier wave theory. The theory may be explained in conjunction with a simplified mathematical model of the auditory system, an it has been confirmed by experimental data as described in applicants article appearing in Alta Frequenza (High Frequency), No. 8, Vol. XXXVII, i968, published by Associazione Elettrotecnicae Elettronica Italiana-A.E.I., Via S. Paolo, Milano.

It should be noted that a universally accepted mathematical model of the auditory system which can interpret all various experimental conditions is not available, and in the absence of such a model applicants simplified model was utilized to confirm the theory and explain the theory based on a qualitative discussion thereof. Assuming that the elements of physiology relating to the human auditory system are known, the auditory system can be mathematically approximated as a unifilar system comprising a mechanical section and a perceptive section. The mechanical section includes the external ear, the internal ear and the cochlea, while the perceptive section includes the organs, synapsis, neuron and central system. By relying on the simplified mathematical model of the auditory system, we have found that if a signal e(t) =e' (t) +e" (t) is applied to the sick ear of a severely or profoundly deaf person, even with only moderate amplification, profoundly deaf persons could acquire an understanding of speech.

In the expression e(t) e' (t) e" (t), e (t) represents the information to be transmitted corresponding to the spoken word. Since this information is generally limited to speech, the information signals are substantially contained within a low frequency range of to 3,000 H; e" (t) represents a suitable periodic high frequency signal of amplitude E" and frequency fp. This signal is referred to as the pseudo-carrier wave. The

pseudo-carrier signals preferably fall within the range of 1,000 H and 3,000 H the exact frequency being dependent somewhat on the profoundly deaf subject, but a high frequency pseudo-carrier up to 5,000 H could also be utilized with a reduction in efficiency.

In accordance with experiments conducted to test applicants pseudo-carrier wave theory, the pseudocarrier was formed of alternate sinusoids or square waves; however, it should be readily apparent to those skilled in the art that other types of periodic signals can also be used for the pseudo-carrier. Using the periodic wave, it has been experimentally proven that the information signal e (I) could be made comprehensible to a profoundly deaf person, even with moderate rates of amplification, when the signal e (t) is summed with a pseudo-carrier and then transformed into corresponding acoustic signals.

BRIEF DESCRIPTION OF THE DRAWINGS It is believed the invention will be more easily understood by reference to the description when considered in connection with the accompanying drawings, wherein:

FIG. 1 is a block diagram or a simplified mathematical model of an auditory system. To this end, the known elements of physiology relating to the human auditory system have been considered as a unifilar system comprising two sections A and B. Section A represents the mechanical portion of the auditory system and includes the external ear, internal ear and cochlea. Section B represents the perceptive portion of the auditory system including the organs, synapsis, and neurons;

FIGS. 2a, 2b and 20 show exemplary oscillograms of signals as they appear at various stages in the block diagram of FIG. 1;

FIG. 3 shows in block diagram form the apparatus embodying the concepts of the present invention; and

FIG. 4 is a schematic diagram of the block diagram arrangement of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT Before proceeding with a complete description of the invention, a definition of symbols appearing in the specification and drawings will be set forth to facilitate an understanding of the description.

e(t) represents the signal applied to a sick ear, i.e., the ear of a profoundly deaf person, and comprises an information signal e (t) summed to a pseudo-carrier signal e" (t).

An apex indicates those quantities where the information signal is present. Two apices indicate those quantities where the pseudo-carrier signal is present. The absence of an apice indicates those quantities where a sum signal is present.

G,,,(s) (wherein s is the complex variable of Leplaces transform) is the transfer function to be allotted to the representative mechanical section A of the auditory system by which function the frequency of an acoustic signal is converted into the chemical stimulus (9 0) which is a derivative to the time of q (t).

q (t) is the amount of chemical exciting material being formed in the auditory system of the subject as a result of the acoustic stimulus;

q,,(t) is the amount of this chemical exciting material in the synapsis determining the tension v(t);

v(t) is the tension between the surfaces of the neuronic membrane, which tension on attaining a threshold value S generates a pulse along the neuron providing for signal u(t) supplied to the central nervous systern;

q,,(t) is the amount of chemical exciting material being decomposed in a time unit proportional to q,,: obviously, q,,(t) is the integral thereof;

q,(t) is the integral amount of energizing material being absorbed for generating the pulse signal u(t). At each pulse all of q in the synapsis is absorbed for this purpose.

Non-linear block NLl takes into account the behaviors of the perceptive organs, whereby q (t) is always positive.

Non-linear block NLZ takes into account the typical threshold operation of the synapsis.

Non-linear block N143 is a pulse generator which is controlled by the signal from block NL2.

Nonlinear block NL4 takes into account the fact that as each time outlet pulse appears along the neuron, the exciting material will disappear at the same time.

C and R are suitable physiological constants of the auditory system. The selection of the physiological constants in the block diagram, function G (s), and identifying mechanism of the central nervous system, should, of course, be based on a reading and correct interpretations of the audiograms for a profoundly deaf person and a person with normal hearing respectively. In the former case, in order that a complete correspondance be provided, it is necessary that the nerve be thought of as formed of a plurality of serial synapsis neuron systems, only some of which are defective, and it is necessary to refer to nerve refractority time, i.e., the time which should necessarily space two nerve pulses, whatever may be the stimulus intensity.

For the quantitative consideration to follow, the above-mentioned simplified block diagram may, however, be regarded as sufficiently approximated to an auditory system to explain applicants pseudo-carrier theory which concludes with the proposition that where the pseudo-carrier is of magnitude E" and of a frequency'fp, even with moderate rates of amplification of signal e (t), the latter will be comprehensible to a profoundly deaf person.

The application of applicants theory to the mathematical model of FIG. 1 is based on several assumptions as stated below. These assumptions generally appear to be reasonable and consistent with some approximations derived from known experimental events:

ASSUMPTIONS A. The auditory system operates according to the block diagramof FIG. 1;

B. The transfer function G,,,(s) referred to a subject is such so as to provide low attenuation in a frequency range from 1,000 to 3,000 H,, while providing much higher attenuation in the frequency range lower than 1,000 Hz. This assumption is justified by a fact reported in the related literature, namely that the basilar membrane can be likened to a resonator (no displacement at and infinite frequency) as well as by the known behavior of some parts of the middle ear;

C. The transfer function G (s) referred to a profoundly deaf subject where his disablements are of the perceptive type is the same as that of a subject having a healthy auditory system. This assumption is a translation into mathematical terms of the medical definition of perceptive lesions in which hearing loss is imputed to the auditory nerve;

D. A set of pulses downstream of the synapsis, following one another at equal intervals of time, are not perceptible by the central nervous system;

B. The addition to an information signal upstream of the synapsis of a constant signal or a signal slightly varying in time does not provide substantial troubles as to a correct reading or interpretation of the information by the central nervous system. These assumptions are primarily justified by examining the mathematics pattern of the operation for the whole auditory system, comprising the blocks diagram arrangement as shown in FIG. 1, all of the blocks being parallel connected between the external ear and central nervous system;

F. The physiological constants for a sick synapsis (threshold rate, constant of decay, etc.) are such as to modify the total transfer function of a profoundly deaf subject (together with the behavior as allotted to the central system with the preceding assumptions) in the sense of providing for a high attenuation beyond 800 l,000 Hz, as usually found in such cases.

On the ground of such assumptions, when supplying the auditory system of a profoundly deaf subject with the pseudo-carrier signal e" (I), the latter, because of its suitably selected frequency, will rrive without any substantial attenuation at the sick synapsis (Assumptions B and C). However, even though of high intensity, this signal cannot pass beyond the sick synapsis in accordance with assumption (F). This signal would effectively provide a voltage v" (t) which, although higher than threshold rate, would provide a signal :4" (t) fonned of pulses which are more or less equally spaced in time (oscillograms of FIGS. 2a and 2b). These signals are not perceptible by the central nervous system owing to assumption (D).

Similary, by supplying only the information or natural signal 2 (I) (mostly formed of low frequency harmonies), the latter arrives at the sick synapsis in an attenuated condition and does not have sufficient energy to pass beyond the relative threshold, even should the amplification thereof be substantial (oscillograms of FIG. 20). Instead, where the sum signal e(t) e (t) e" (t) is supplied, it will'produce a chemical excitation in the central nervous system corresponding to:

Where, due to an undampened or unattenuated signal v" (t), the sum signal is such as to pass beyond the threshold of a sick synapsis, a signal u(t) will be provided downstream of the sick synapsis. On the ground of assumption (D), signal u(t) may be thought of as construed by the central nervous system as corresponding to signal v (1) only, or relating to the information signal.

Summarizing the foregoing, it may be stated synthetically that the psuedo-carrier signal will provide a sufficient energy so that the information signal might pass beyond the synapsis of the sick nerve while, on the other hand, its comparatively high and periodic frequency would prevent any interference with information in the signal.

Referring now to the block diagram of the apparatus a shown in FIG. 3, there is provided an oscillator 1 adapted to provide the periodic signal e" (t). A transducer device 2 transforms the acoustic information signals into corresponding electric signals e (2). Summer 3 sums signals e (t) and e" (t) entering it so as to provide for signals e(t) which are fed or translated to an amplifier 4. The output of amplifier 4 is connected to a device 5 for transforming the electric signals into corresponding acoustic signals.

A further way to attain the same purpose, that is, to take advantage of the energy of a high frequency pseudo-carn'er in order that information signal e (t) passed beyond the sick thresholds, may be to uniformly aniplify the low frequency information signal and to add the required energy by highly amplifying signal 2' (t) within a narrow high frequency range so as to automatically obtain the pseudo-carrier from said information signal.

FIG. 4 shows the complete electric diagram of the circuit apt to obtain the mixing of the two signals, one is the audio signal, or information signal from the microphone after a suitable amplification, and the other is produced by a local oscillator and has a variable frequency as illustrated in FIG. 3. The circuit comprises a variable frequency oscillator 1, a sum node 3, that is a point where the audio signal and the local signal flow in and overlap and a final power amplifier 4.

Oscillator 1 is free running multivibrator and is carried out by means of a conventional integrated circuit, for example, of RTL 910 type.

Resistors R R and condensers C C determine the minima frequency of oscillation, while R and C assure the automatic firing or starting of the oscillation itself, whose frequency can be adjusted by means of the unit constituted by potentiometer P, resistors R R and diodes D D The signal produced by the oscillator is applied at the inlet of the final amplifier 4 by means of condenser resistor unit C,,, R The audio signal arrives to the same amplifier 4 through condenser-resistor unit CB RB.

In the node 3 (sum node) there is a composite signal, resulting from the sum of the local signal and the audio one, which is amplified by the final stage and sent to the outlet and from here to the device 5 for transforming the electric signal to an acoustic signal.

The ampltude of the single signals which flow onto node 3 can be adjusted independently by varying the arm position of potentiometers P and P The final amplifier 4 is complementary symmetry type. Resistors R and R determine the working point biasing of the transistors while the other components are necessary for proper operation of the amplifier itself.

Condenser C placed between amplifier 4 and outlet terminal serves to block the direct or unidirectional component due to the biasing of the transistors, but it permits only the passage of the alternate signal necessary for producing the sound.

By the values indicated as an example, in the diagram, the oscillation frequency can be varied between about l kHz and 5 kHz, while the voltage gain of the amplifier is about 3.

That which is claimed is:

l. A method to obtain a sound signal comprehensible to a deaf person, said method comprising the following steps:

transforming an acoustic information signal into a corresponding main electrical signal;

generating a second electrical signal from a local oscillator, said second electrical signal being free of acoustic information, unmodulated and having a frequency higher than that of said main electrical signal;

adding the second signal to the main electrical signal by linear mixing, thus obtaining a composite electrical signal; and producing a corresponding sound signal from said composite electrical signal, which sound signal passes beyond the thresholds of the deaf persons auditory system, to make the deaf person receive the content of said acoustic information signal in an intelligible form.

2. A method according to claim 1, wherein said acoustic information signal signal has a frequency in the range of 0-3 kHz and said second electrical signal has a frequency in the range of 1 kHz to 5 kHz.

3. A method according to claim 1, further including the step of amplifying said composite electrical signal and translating said amplified signal to the auditory system of the deaf person.

4. An electronic apparatus adapted to make a sound signal intelligible to a deaf person comprising an electro-acoustic transducer arranged to transform the sound signal into a corresponding main electrical signal, local oscillator means for supplying a second, unmodulated electrical signal, said transducer and oscillator being connected at the input of an amplifier for obtaining by linear mixing a composite signal, comprising the sum of said main and said second, unmodulated electrical signal, and means connecting the output of the amplifier to a second electro-acoustic transducer arranged to transform the amplified composite signal into a corresponding sound signal adapted to be translated to the deaf person.

5. Apparatus as set forth in claim 4, wherein said oscillator is operatively arranged to provide a periodic signal having a frequency between 1 kHz and 5 kHz.

"H050 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIQN Patent NO. 3,781,491 Dated December 25, 1973 Inventoflw Emanuele Biondi and Leonardo Biondi It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading page of the patent insert the following:

[30] FOREIGN APPLICATION PRIORITY DATA March 29, 1968 Italy 14, 550

Signed and sealed this 20th day of August 197 E Attest:

McCOY M. GIBSON, JR. C. MARSHALL Dl-QNN Commissioner of Patents Attesting Officer 

1. A method to obtain a sound signal comprehensible to a deaf person, said method comprising the following steps: transforming an acoustic information signal into a corresponding main electrical signal; generating a second electrical signal from a local oscillator, said second electrical signal being free of acoustic information, unmodulated and having a frequency higher than that of said main electrical signal; adding the second signal to the main electrical signal by linear mixing, thus obtaining a composite electrical signal; and producing a corresponding sound signal from said composite electrical signal, which sound signal passes beyond the thresholds of the deaf person''s auditory system, to make the deaf person receive the content of said acoustic information signal in an intelligible form.
 2. A method according to claim 1, wherein said acoustic information signal signal has a frequency in the range of 0-3 kHz and said second electrical signal has a frequency in the range of 1 kHz to 5 kHz.
 3. A method according to claim 1, further including the step of amplifying said composite electrical signal and translating said amplified signal to the auditory system of the deaf person.
 4. An electronic apparatus adapted to make a sound signal intelligible to a deaf person comprising an electro-acoustic transducer arranged to transform the sound signal into a corresponding main electrical signal, local oscillator means for supplying a second, unmodulated electrical signal, said transducer and oscillator being connected at the input of an amplifier for obtaining by linear mixing a composite Signal, comprising the sum of said main and said second, unmodulated electrical signal, and means connecting the output of the amplifier to a second electro-acoustic transducer arranged to transform the amplified composite signal into a corresponding sound signal adapted to be translated to the deaf person.
 5. Apparatus as set forth in claim 4, wherein said oscillator is operatively arranged to provide a periodic signal having a frequency between 1 kHz and 5 kHz. 